The practice of ellipsometry is well established as a non-destructive approach to determining characteristics of sample systems, and can be practiced in real time. The topic is well described in a number of publications, one such publication being a review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum., 61(8) (1990).
In general, modern practice of ellipsometry typically involves causing a spectroscopic beam of electromagnetic radiation, in a known state of polarization, to interact with a sample system at least one angle of incidence with respect to a normal to a surface thereof, in a plane of incidence. (Note, a plane of incidence contains both a normal to a surface of an investigated sample system and the locus of said beam of electromagnetic radiation). Changes in the polarization state of said beam of electromagnetic radiation which occur as a result of said interaction with said sample system are indicative of the structure and composition of said sample system. The practice of ellipsometry further involves proposing a mathematical model of the ellipsometer system and the sample system investigated by use thereof, and experimental data is then obtained by application of the ellipsometer system. This is typically followed by application of a square error reducing mathematical regression to the end that parameters in the mathematical model which characterize the sample system are evaluated, such that the obtained experimental data, and values calculated by use of the mathematical model, are essentially the same.
A typical goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a sample system, sample system characterizing PSI and DELTA values, (where PSI is related to a change in a ratio of magnitudes of orthogonal components rp/rs in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components rp and rs), caused by interaction with said sample system. The basic equation relating PSI and DELTA is:ρ=rp/rs−Tan(Ψ)exp(iΔ)
As alluded to, the practice of ellipsometry requires that a mathematical model be derived and provided for a sample system and for the ellipsometer system being applied. In that light it must be appreciated that an ellipsometer system which is applied to investigate a sample system is, generally, sequentially comprised of:                a. a Source of a beam electromagnetic radiation;        b. a Polarizer element;        c. optionally a compensator element;        d. (additional element(s));        e. a sample system;        f. (additional element(s));        g. optionally a compensator element;        h. an Analyzer element; and        i. a Spectroscopic Detector System.Each of said components b.-i. must be accurately represented by a mathematical model of the ellipsometer system along with a vector which represents a beam of electromagnetic radiation provided from said source of a beam electromagnetic radiation, Identified in a. above)        
Various conventional ellipsometer configurations provide that a Polarizer, Analyzer and/or Compensator(s) can be rotated during data acquisition, and are describe variously as Rotating Polarizer (RPE), Rotating Analyzer (RAE) and Rotating Compensator (RCE) Ellipsometer Systems. As described elsewhere in this Specification, the present invention provides that no element must be continuously rotated during data acquisition but rather that a sequence of discrete polarization states can be imposed during data acquisition. This approach allows eliminating many costly components from conventional rotating element ellipsometer systems, and, hence, production of an “Ultra-Low-Complexity” ellipsometer system. It is noted, that nulling ellipsometers also exist in which elements therein are rotatable in use, rather than rotating. Generally, use of a nulling ellipsometer system involves imposing a linear polarization state on a beam of electromagnetic radiation with a polarizer, causing the resulting polarized beam of electromagnetic radiation to interact with a sample system, and then adjusting an analyzer to an azimuthal azimuthal angle which effectively cancels out the beam of electromagnetic radiation which proceeds past the sample system. The azimuthal angle of the analyzer at which nulling occurs provides insight to properties of the sample system.
It is further noted that reflectometer systems are generally sequentially comprised of:                a. a Source of a beam electromagnetic radiation;        d. (optional additional element(s));        e. a sample system;        f. (optional additional element(s));        i. a Spectroscopic Detector System;and that reflectometer systems monitor changes in intensity of a beam of electromagnetic radiation caused to interact with a sample system. That is, the ratio of, and phase angle between, orthogonal components in a polarized beam are not of direct concern.        
Continuing, in use, data sets can be obtained with an ellipsometer system configured with a sample system present, sequentially for cases where other sample systems are present, and where an ellipsometer system is configured in a straight-through configuration wherein a beam of electromagnetic radiation is caused to pass straight through the ellipsometer system without interacting with a sample system. Simultaneous mathematical regression utilizing multiple data sets can allow evaluation of sample system characterizing PSI and DELTA values over a range of wavelengths. The obtaining of numerous data sets with an ellipsometer system configured with, for instance, a sequence of sample systems present and/or wherein a sequential plurality of polarization states are imposed on an electromagnetic beam caused to interact therewith, can allow system calibration of numerous ellipsometer system variables.
Patents of which the Inventor is aware include those to Woollam et al, U.S. Pat. No. 5,373,359, patent to Johs et al. U.S. Pat. No. 5,666,201 and patent to Green et al., U.S. Pat. No. 5,521,706, and patent to Johs et al., U.S. Pat. No. 5,504,582 are disclosed for general information as they pertain to ellipsometer systems.
Further patents of which the Inventor is aware include U.S. Pat. Nos. 5,757,494 and 5,956,145 to Green et al., in which are taught a method for extending the range of Rotating Analyzer/Polarizer ellipsometer systems to allow measurement of DELTA'S near zero (0.0) and one-hundred-eighty (180) degrees, and the extension of modulator element ellipsometers to PSI'S of forty-five (45) degrees. Said patents describes the presence of a variable, transmissive, bi-refringent component which is added, and the application thereof during data acquisition to enable the identified capability.
A patent to Thompson et al. U.S. Pat. No. 5,706,212 is also disclosed as it teaches a mathematical regression based double Fourier series ellipsometer calibration procedure for application, primarily, in calibrating ellipsometers system utilized in infrared wavelength range. Bi-refringent, transmissive window-like compensators are described as present in the system thereof, and discussion of correlation of retardations entered by sequentially adjacent elements which do not rotate with respect to one another during data acquisition is described therein.
A patent to He et al., U.S. Pat. No. 5,963,327 is disclosed as it describes an ellipsometer system which enables providing a polarized beam of electromagnetic radiation at an oblique angle-of-incidence to a sample system in a small spot area.
A patent to Johs et al., U.S. Pat. No. 5,872,630 is disclosed as it describes an ellipsometer system in which an analyzer and polarizer are maintained in a fixed in position during data acquisition, while a compensator is caused to continuously rotate.
Patent to Dill et al., U.S. Pat. No. 4,953,232 is disclosed as it describes a rotating compensator ellipsometer system.
Patents co-owned with this application, which patents Claim various Compensator Designs recited in Claims herein, and which patents are incorporated hereinto by reference are:                U.S. Pat. No. 5,946,098 to Johs et al.;        U.S. Pat. No. 5,963,325 to Johs et al.;        U.S. Pat. No. 6,084,674 to Johs et al.;        U.S. Pat. No. 6,084,675 to Herzinger et al.;        U.S. Pat. No. 6,100,981 to Johs et al.;        U.S. Pat. No. 6,118,537 to Johs et al.;        U.S. Pat. No. 6,141,102 to Johs et al.Patents cited in examination of said patents included U.S. Pat. No. 4,556,292 to Mathyssek et al. and U.S. Pat. No. 5,475,525 to Tournois et al.        
A patent to Coates et al., U.S. Pat. No. 4,826,321 is disclosed as it describes applying a reflected monochromatic beam of plane polarized electromagnetic radiation at a Brewster angle of incidence to a sample substrate to determine the thickness of a thin film thereupon.
Other patents which describe use of reflected electromagnetic radiation to investigate sample systems are Nos. RE 34,783, U.S. Pat. No. 4,373,817, and U.S. Pat. No. 5,045,704 to Coates; and U.S. Pat. No. 5,452,091 to Johnson.
A patent to Bjork et al., U.S. Pat. No. 4,647,207 is disclosed as it describes an ellipsometer system which has provision for sequentially positioning a plurality of reflective polarization state modifiers in a beam of electromagnetic radiation. While said 207 patent mentions investigating a sample system in a transmission mode, no mention or suggestion is found for utilizing a plurality of transmitting polarization state modifiers, emphasis added. U.S. Pat. No. 4,210,401; 4,332,476 and 4,355,903 are also identified as being cited in the 207 patent. It is noted that systems as disclosed in these patents, (particularly in the 476 patent), which utilize reflection from an element to modify a polarization state can, that if such an element is an essential duplicate of an investigated sample and is rotated ninety degrees therefrom, then the effect of the polarization state modifying element on the electromagnetic beam effect is extinguished by the sample.
A patent to Mansuripur et al., U.S. Pat. No. 4,838,695 is disclosed as it describes an apparatus for measuring reflectivity.
Patents to Rosencwaig et al., U.S. Pat. Nos. 4,750,822 and 5,595,406 are also identified as they describe systems which impinge electromagnetic beams onto sample systems at oblique angles of incidence. The 406 patent provides for use of multiple wavelengths and multiple angles of incidence. For similar reasons U.S. Pat. No. 5,042,951 to Gold et al. is also disclosed.
A patent to Osterberg, U.S. Pat. No. 2,700,918 describes a microscope with variable means for increasing the visibility of optical images, partially comprised of discrete bi-refringent plates which can be positioned in the pathway between an eyepiece and an observed object. Other patents identified in a Search which identified said 918 patent are U.S. Pat. No. 3,183,763 to Koester; U.S. Pat. No. 4,105,338 to Kuroha; U.S. Pat. No. 3,992,104 to Watanabe and a Russian Patent, No. SU 1518728. Said other patents are not believed to be particularly relevant, however.
A patent, U.S. Pat. No. 5,329,357 to Bernoux et al. is also identified as it Claims use of fiber optics to carry electromagnetic radiation to and from an ellipsometer system which has at least one polarizer or analyzer which rotates during data acquisition. It is noted that if both the polarizer and analyzer are stationary during data acquisition that this patent is not controlling where electromagnetic radiation carrying fiber optics are present.
Patents identified in a Search specifically focused on the use of lenses, preferrably achromatic, in ellipsometry and related systems are:                U.S. Pat. Nos. 5,877,859 and 5,798,837 to Aspnes et al.;        U.S. Pat. No. 5,333,052 to Finarov;        U.S. Pat. No. 5,608,526 to Piwonka-Corle et al.;        U.S. Pat. No. 5,793,480 to Lacy et al.;        U.S. Pat. Nos. 4,636,075 and 4,893,932 to Knollenberg; and        U.S. Pat. No. 4,668,860 to Anthon.        
A patent, U.S. Pat. No. 5,917,594 to Norton describes a system which utilizes a spherical mirror to focus an electromagentic beam onto the surface of a sample in the form of a small spot. A relevant aspect of the 594 patent system is that a positive lens and a negative meniscus lens are combined and placed into the pathway of the electromagnetic beam prior to its reflection from a focusing spherical mirror. The purpose of doing so is to make the optical system, as a whole, essentially achromatic in the visible wavelength range, and even into the ultraviolet wavelength range. It is further stated that the power of the combined positive lens and negative meniscus lens is preferrably zero.
Additional patents, which provide insight to reflective optics are disclosed below.
Patents to Coates U.S. Pat. No. 5,045,704 and RE: 34,783, for example, describe a system which applies a reflective objective lens to direct electromagnetic radiation provided to it by a convex reflective element to a spot on a sample. Said electromagnetic radiation is provided to said convex reflective element via a beam splitter. It is noted that the concave reflective objective lens disclosed in said Coates patents is of a donut shape, which can be more difficult to manufacture than a plurality of spherical concave mirrors.
Additional patents to Norton et al. include U.S. Pat. Nos. 5,486,701 and 5,859,424, and a patent to Piwonka-Corle et al., U.S. Pat. No. 5,608,526. Said patents describe use of spherical reflective focusing elements to converge a beam of electromagnetic radiation into a small spot on a sample.
U.S. Pat. No. 6,744,505 B1 to Wang et al. is disclosed as it describes use of a concave reflecting optics to direct diverging diffracted electromagnetic radiation into a collimated beam which enters a detector. Further disclosed is a Published Application of Wang et al. is U.S. Pat. No. 2004/0125369 A1.
U.S. Pat. No. 3,748,015 to Offner is disclosed as it describes an imaging system comprising a concave spherical mirror and a convex spherical mirror; said elements being arranged such that electromagnetic radiation caused to approach the concave spherical reflects at a first location thereon is reflected to said a convex spherical mirror, from which it reflects onto a second location of said concave spherical mirror, from which it reflects as a beam of electromagnetic radiation, which, if the electromagnetic radiation caused to approach the concave spherical mirror at a first location was, for instance, an imaged aperture, appears as a small spot on the sample. It is emphasized that a collimated electromagnetic beam is not “focused” by the 1:1 imager, but rather a substantially point source is imaged thereby.
Patents identified by the Examiner in examination of the Parent application Ser. No. 10/928,904 are: U.S. Pat. No. 4,650,315 to Markle; U.S. Pat. No. 6,835,933 to Lin et al.; U.S. Pat. No. 5,136,413 to MacDonald et al.; U.S. Pat. No. 4,688,904 to Hirose et al.; U.S. Pat. No. 6,141,100 to Burka et al. U.S. Pat. No. 6,522,404 to Wilson et al.; U.S. Pat. No. 5,880,834 to Chrisp; U.S. Pat. No. 6,600,560 to Mikkelsen et al.; U.S. Pat. No. 6,522,717 to Murakami et al.; U.S. Pat. No. 5,715,061 to Fujiwara; EPO 0 452 963 A2 BY Diapon Screen Mfg. Co.
An additional clever combination of refractive and reflective optics to provide aberation corrected small spots of electromagnetic radiation onto samples would provide utility, particularly if it allowed selection of angles-of-incidence at which a beam impinges on a sample, and even in view of relevant prior art, there remains need for a spectroscopic ellipsometer system which:                presents with a source of spectroscopic electromagnetic radiation and a spectroscopic multi-element detector system;        comprises polarizer and analyzer which remain stationary during data acquisition;        utilizes a plurality of transmissive step-wise rotatable or rotating compensator means to effect a plurality of sequential polarization states during said data acquisition;        which includes at least one reflective optics for focusing electromagnetic radiation onto a spot on a sample, simultaneously or sequentially at a plurality of angles-of-incidence and;        which comprise at least one transmissive abberation correction means.        
In particular, need ramains for a system comprising reflective optics in the context of rotating or rotatable compensator ellipsometer and the like systems as were taught originally in U.S. Pat. No. 5,872,630 to Johs et al., from which this application is a CIP. The present invention provides a system with the identified attributes.